Strain engineering aims for room-temp superconducting

PORTLAND, Ore.  Strain-correlated electron materials can be conductors, semiconductors or insulators depending on how much strain is engineered into their structure. As a new type of transition-metal oxide, correlated electron materials could allow the selective placement of strain to alter the spatial arrangement of its crystalline lattice, according to researchers at Lawrence Berkeley National Laboratory.

The Energy Department lab recently created structural irregularities called phase inhomogeneity in correlated electron materials that could someday enable colossal magnetoresistance, and perhaps even room-temperature superconductivity.

Correlated electron materials, as the name implies, exhibit correlated electron capabilities at room temperature that otherwise might require a phase change, such as by super cooling a superconducting material. By engineering the right kind of strain into a correlated electron material, designers could theoretically endow them with extraordinary room-temperature characteristics.

Berkeley Lab's Materials Sciences Division and the University of California at Berkeley's Department of Materials Science and Engineering, led by physicist Junqiao Wu, demonstrated selective placement of strain in vanadium oxide microwires. This technique changed its electronic phase from conductor to semiconductor to insulator.

Scientists have debated whether phase inhomogeneity could be generated by external sources of strain, but the Berkeley Labs researchers claimed to have validated the process with optical images of a multiple-domain vanadium oxide microwires showing pure insulating on top and pure metallic on the bottom, co-existing with metallic/insulating phases in between.

Like low-temperature superconductors, whose lattice structure changes to allow electrons to flow without resistance, similar quantum effects allowing collective actions by electrons can be induced by strain into correlated electron materials. Likewise, magnetoresistance results from changes in the crystalline lattice whereby the effect of a magnetic field is to vastly increase the electrical resistance of the correlated electron material.

Wu also speculated that by fabricating nanowires atop a piezoelectric material, the electron phase of the vanadium oxide nanowires could be controllled electrically, permitting circuits to be rewired on-the-fly.

Funding for the research was provided by the National Science Foundation.